What are some values from Holes by Louis Sachar?

Justice, of course, is a major theme of the book, but Sachar's treatment of this theme calls into question the validity of criminal justice institutions—the camp—and suggests that true justice is the product of personal morality. This can be seen by comparing the treatment of the boys at the hands of the corrupt "professionals" who run the camp with the boys' treatment of one another. More specifically, the boys' ability to treat each other with genuine kindness can be seen in the bond that develops between Stanley and Zero after Stanley begins to teach Zero to read.
Truth, or personal integrity, is another major theme in the book. While Stanley's decision to steal the water truck is, in one sense, a crime, in a larger sense the risk he takes in doing so is an expression of his own moral code: he feels an obligation to search for Zero. On another level, the "truth" about the camp and why the boys are digging the holes is another example of how appearances can be deceiving. The camp is not really concerned about juvenile corrections; the warden is not really concerned about the inmates; the boys are not criminals but, in actuality, victims.
A final theme would be fate. The story suggests that what happens to Stanley and Zero has been preordained somehow. Sam's lynching is the primary act of injustice that sets the plot in motion: it not only causes Kate to turn into a bandit and bury her loot, it actually creates the landscape of the camp (after the lynching, the lake mysteriously dries up). It seems only fitting that both Stanley and the warden had ancestors who searched for the treasure, that it is Kate's hundred-year-old preserves that keep Stanley alive in the desert, and that Stanley ultimately is the one to prevail over the warden.

One value reflected in the book Holes is the importance of friendship. In the book, there is a tremendous value placed on friendship. Stanley actually becomes quite happy with his situation (despite it still being dangerous) once his friendship with Zero is solidified.  
Another value present in the book is justice. That might seem odd at first because the book starts with Stanley being punished for a crime that he didn't commit. There doesn't seem to be any working legal justice. As the story continues, though, readers see a strong sense of moral justice among many of the boys at Camp Green Lake. They know they are being unfairly treated, and there is a sense of moral outrage at the severity of the punishments based on the minor crimes they committed. They know justice is not being properly served.  
Perhaps I can take the justice value further. By the end of the book, everything is set right. Good people are rewarded and evil people are punished. It's as if the universe itself willed justice to be done. Call it fate or cosmic justice, but it still happened.